|Messier 14 in Ophiuchus.|
M14 is known to contain 70 variable stars, quite a decent number for a globular cluster. In 1938 a nova went off in the cluster, but this fact was not discovered for 28 years until photos of the cluster taken in 1938 were examined in 1964. It's estimated from these photos that the nova reached a peak brightness over 5 times that of the brightest non-nova stars in the cluster. This is only the second nova known to have appeared in a globular cluster (and the first was in 1860, before it could be photographed).